jb@miner0:~$ atitweak -s -A 0 ; atitweak -s -A 2
0. AMD Radeon HD 6900 Series (:0.0)
    engine clock 946MHz, memory clock 821MHz, core voltage 1.15VDC, performance level 2, utilization 99%
    fan speed 72% (4259 RPM) (user-defined)
    temperature 73 C
2. AMD Radeon HD 6900 Series (:0.2)
    engine clock 946MHz, memory clock 821MHz, core voltage 1.175VDC, performance level 2, utilization 99%
    fan speed 72% (4249 RPM) (user-defined)
    temperature 73 C


I do not overclock the cards higher than what AMDOverdriveCtrl would be able to do.  In fact, once I found my highest hash (~414) at 946MHz, I then proceeded to undervolt the card.  Both cards use the same profile, but strangely enough the core voltage on #2 is different than #0.  I'll have to look into that.